Fast control of DNA replication in response to hypoxia and to inhibited protein synthesis in CCRF-CEM and HeLa cells

In order to elucidate whether data about the fast regulation of DNA replica tion in dependence on oxygen supply and on a functioning protein synthesis, previously elaborated with Ehrlich ascites cells, are valid for human cell s too, we repeated key experiments with CCRF-CEM and HeLa cells. The most i mportant techniques employed were DNA fibre autoradiography and alkaline se dimentation analyses of growing (pulse-labeled) daughter strand DNA, It was found that CCRF-CEM and HeLa cells responded to transient hypoxia and to t ransient inhibition of protein synthesis in an almost identical fashion, Sc heduled replicon initiations were reversibly suppressed and the progress ra tes of replication forks, which were already active before the respective i nhibitory conditions were established, were reversibly slowed down. The inc lusion of the fork progress rate in the response differs from Ehrlich ascit es cells, which respond only by suppressing initiation. Further circumstanc es of the fast oxygen dependent response, concerning the behaviour of ribon ucleotide reductase and of the dNTP pools, revealed no significant differen ces among the three cell lines. The striking identity of the response of ea ch of the cell lines to hypoxia and to inhibited protein synthesis prompts the suspicion that converging fast regulatory pathways act on the cellular replication machinery, The phenomena as such seem to be rather widespread a mong mammalian cells.